Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Indirectly Heated Valve (Tube) Longevity Question.  (Read 528 times)
MM0IMC
Member

Posts: 68




Ignore
« on: December 06, 2017, 05:46:18 AM »

Hi folks,

Can anyone tell me if repeated on-off cycling (normal daily use) of an amplifier using an indirectly heated valve (tube) can shorten the life of the valve (tube), please? The amplifier uses a Russian NOS GU-74B tetrode.

73,

Ian - MM0IMC.
Logged
VK3BL
Member

Posts: 1355


WWW

Ignore
« Reply #1 on: December 10, 2017, 05:09:23 AM »

Hi folks,

Can anyone tell me if repeated on-off cycling (normal daily use) of an amplifier using an indirectly heated valve (tube) can shorten the life of the valve (tube), please? The amplifier uses a Russian NOS GU-74B tetrode.

73,

Ian - MM0IMC.

Doubtful.  I never snapped a filament in any 811A or 572B, but I sure as heck burnt through plenty in mere months leaving them running in standby.

Turn it off if you're not going to use it within 30 minutes; only turn it on if its Rare DX or you have too.

If you want to leave the amp on whilst at work, or 'just because', solid state pays for itself quite quickly, even if you occasionally blow some FETs.
Logged

J.D. Mitchell - VK3BL / XU7AGA - http://vk3bl.wordpress.com
N3QE
Member

Posts: 4921




Ignore
« Reply #2 on: December 10, 2017, 12:22:56 PM »

Can anyone tell me if repeated on-off cycling (normal daily use) of an amplifier using an indirectly heated valve (tube) can shorten the life of the valve (tube), please? The amplifier uses a Russian NOS GU-74B tetrode.

There is no risk to tube life in on-off cycling a GU74B or most other ceramic tubes.

Most oxide coated cathodes are rated for overall power-on hours of 10,000 to 20,000 hours. I don't know the exact rating for the GU74B but considering its original military application it is very doubtful to be longer than 20,000 hours. 20,000 hours is about 2 years 24x7.



Logged
KM1H
Member

Posts: 2598




Ignore
« Reply #3 on: Yesterday at 12:15:12 PM »

The Russians are happy if they make 1000 hours
https://frank.pocnet.net/sheets/018/g/GU74B.pdf

In commercial ham amps they are run way over spec and called the 4CX-800A and often go flat in 2-3 years of heavy use of excessive power. Run by the spec of 600W PD and 550W per tube output and they may last a long time.

Carl
Logged
K6AER
Member

Posts: 4682




Ignore
« Reply #4 on: Yesterday at 05:22:09 PM »

I have found the Russian Gu-74B's in the Alpha 87A will last a very long time if the power is limited to 1500 watts out. The tube will as Carl had mentioned go soft if abused or you try to get 2300 watts out in the contest mindset mode. My 87A backup amp is performing on the Russian tubes for the 8th year.
Logged
KE2TR
Member

Posts: 622




Ignore
« Reply #5 on: Yesterday at 08:03:57 PM »

You all seem to have lots of experience with the Russian tubes, W8JI has dowm played them for years over the old gold standard Eimac tubes but I remember Eimac did have a few years back in the 1980ies were there 8877 was having more than a few problems with new production tubes. Threw the years I have run amp's with 8877 tubes without issue, never had one go bad even if a guest op didn't know about grid current and have never seen one go soft at 1500W out during any contest but have never done RTTY contest. I have also owned the Alpha hybrid 91b for over 6 years during my contest time when we built W2A station and ran them at 1500W all weekend long year after year and never seen any loss of output on two of those amps but I have seen friends with Alpha 87A have those 3CX800A pop like candy after a few years at 1500W.
I have also know fellows run those 91B amps with the GU74B tubes flat out at 2.5K and have never replaced those tubes, maybe they got a good pair not the crap that is un tested from some internet tube hustler. How long tubes last depends on were they are purchased from  plus incorrect operating practices but starting old wives tales just because the tube was made in Russia but China is another story cause they need to go threw production changes which takes years for them to get it right.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!